This chapter discusses the effect of composition and cooling rate on the microstructure and properties of cast irons and explains how they differ from steel. It describes the conditions under which white, gray, mottled (chilled), and nodular (ductile) cast irons are produced, and examines the growth mechanisms and structural details that set them apart. It also discusses the formation of compacted (vermicular) graphite and malleable iron, and compares and contrasts the composition, properties, and heat treatment of whiteheart and blackheart malleable types.

The commercial relevance of cast irons is best understood in the context of the iron-carbon phase diagram, where their composition places them near the eutectic point, which sheds light on why they melt at lower temperatures than steel and why they can be cast into more intricate shapes. This chapter examines these unique properties and how they are derived. It begins by describing the basic metallurgy of cast iron, focusing on the eutectic reaction. It explains how to control the reaction and thus properties of cast iron by overcooling and inoculation. The chapter also discusses composition, microstructure, heat treatments, and the classification and casting characteristics of white, gray, ductile, malleable, compacted graphite, and special cast irons.

The properties of cast iron are determined primarily by the form of carbon they contain, which in turn, is controlled by modifying compositions and cooling rates during casting. Certain alloys (such as Si, Al, Ni, Co, and Cu) promote graphite formation, while others (such as S, V, Cr, Sn, Mo, and Mn) promote the formation of cementite. This chapter examines the relative potencies of these alloys and their effect on microstructure. It covers the five most common commercial cast irons, including white, gray, ductile, malleable, and compacted graphite, describing their compositional ranges, distinguishing features, advantages, limitations, and applications.

This article discusses the metallurgy and properties of ductile cast iron. It begins with an overview of ductile or spheroidal-graphite iron, describing the specifications, applications, and compositions. It then discusses the importance of composition control and explains how various alloying elements affect the properties, behaviors, and processing characteristics of ductile iron. The article describes the benefits of nickel and silicon additions in particular detail, explaining how they make ductile iron more resistant to corrosion, heat, and wear.

This article explains how malleable iron is produced and how its microstructure and properties differ from those of gray and ductile iron. Malleable iron is first cast as white iron then annealed to convert the iron carbide into irregularly shaped graphite particles called temper carbon. Although malleable iron has largely been replaced by ductile iron, the article explains that it is still sometimes preferred for thin-section castings that require maximum machinability and wear resistance. The article also discusses the annealing and alloying processes by which these properties are achieved.

This article discusses the composition and morphology of compacted graphite (CG) iron relative to that of gray and ductile iron. It explains that the graphite in CG iron is intermediate in shape between the spheroidal graphite found in ductile iron and the flake graphite in gray iron, giving it distinct advantages in a number of applications. The article also discusses the role of melt treatment elements and explains how alloying and heat treatment affect tensile strength, hardness, toughness, and ductility.

This chapter discusses the causes and effects of ductile and brittle fracture and their key differences. It describes the characteristics of ductile fracture, explaining how microvoids develop and coalesce into larger cavities that are rapidly pulled apart, leaving bowl-shaped voids or dimples on each side of the fracture surface. It includes SEM images showing how the cavities form, how they progress to final failure, and how dimples vary in shape based on loading conditions. The chapter, likewise, describes the characteristics of brittle fracture, explaining why it occurs and how it appears under various levels of magnification. It also discusses the ductile-to-brittle transition observed in steel, the characteristics of intergranular fracture, and the causes of embrittlement.

In order to understand how various types of single-load fractures are caused, one must understand the forces acting on the metals and also the characteristics of the metals themselves. All fractures are caused by stresses. Stress systems are best studied by examining free-body diagrams, which are simplified models of complex stress systems. Free-body diagrams of shafts in the pure types of loading (tension, torsion, and compression) are the simplest; they then can be related to more complex types of loading. This chapter discusses the principles of these simplest loading systems in ductile and brittle metals.

This chapter discusses ferrous metals, including low-carbon steels, stainless steels, and cast irons. It also provides information on hardening and hardenability and the tempering process.

This chapter examines the isothermal phase transformations of the iron-carbide system. The discussion includes the formation of ferritic, eutectoid, hypoeutectoid, hypereutectoid, bainitic, and martensitic microstructures as well as their properties, composition, and metallurgy. The use of time-temperature-transformation (TTT) diagrams in understanding the phase transformations and the changes in the isothermal transformation curves due to the addition of carbon and other alloying elements are also discussed.

This chapter discusses the composition, properties, microstructure, grain formation, and fracture behavior of gray, white, ductile, and malleable cast iron and how these critical factors are affected when iron is heated to different temperatures prior to or during solidification.

This chapter is a detailed account of heat treating techniques for cast irons (gray and ductile), providing the reader with a basic understanding of the differences among various types of cast irons and the concept of carbon equivalent. The types of heat treatments discussed are stress relieving, annealing, normalizing, surface hardening, quenching, martempering, austempering, and flame and induction hardening.

Cast irons, like steels, are iron-carbon alloys but with higher carbon levels than steels to take advantage of eutectic solidification in the binary iron-carbon system. Like steel, heat treatment of cast iron includes stress relieving, annealing, normalizing, through hardening, and surface hardening. This chapter introduces solid-state heat treatment of iron castings, covering general considerations for heat treatment and discussing the processes, advantages, and disadvantages of heat treatment of cast iron.

This chapter introduces the metallographer to the various types of steels and cast irons and explains how they are classified and defined. Classification and designation details are provided for plain carbon steels, alloy steels, and gray, white, ductile, and malleable cast irons.

This article covers the metallurgy and properties of gray irons. It describes the classes or grades of gray iron, the types of applications for which they are suited, and the corresponding compositional ranges. It discusses the role of major, minor, and trace elements, how they are added, and how they affect various properties, behaviors, and processing characteristics. It explains how silicon, chromium, and nickel, in particular, improve high-temperature, corrosion, and wear performance.

Carbon and low-alloy steels in high-temperature service are vulnerable to the effects of hydrogen attack, which include severe loss in tensile and rupture strengths as well as ductility. As the chapter explains, when steel is in contact with hydrogen molecules at elevated temperatures, hydrogen atoms can be absorbed at the surface and then diffuse into the metal. Hydrogen atoms in the metal then react with iron carbide forming methane gas which can accumulate at grain boundaries and other interfaces. The chapter describes two applications, one in coal-fired boilers, the other in petroleum refining, where hydrogen attack was observed. It documents the extent of the damage in each case and identifies the source of the hydrogen.

Induction hardened steels are often tempered to increase their ductility and relieve quenching stresses. During tempering, martensitic microstructures supersaturated with carbon decompose into a more stable, ductile form. This chapter discusses the transformations associated with the tempering process and their effect on ductility as well as other properties. It describes the structural and compositional changes that occur during the four stages of tempering, the relative influence of time and temperature, and how tempering affects the hardness of various grades of steel. The chapter discusses the practice of both furnace and induction tempering, describing where and how they are used, their tempering characteristics, strengths and limitations, and operating parameters. It also discusses the use of residual heat tempering, a self-tempering process.

The mechanical behavior of a material is its response to an applied load or force. Important mechanical properties are strength, hardness, stiffness, and ductility. This chapter discusses three principal ways in which these properties are tested: tension, compression, and shear. Important tensile properties that can be determined by the tensile test include yield strength, ultimate tensile strength, ductility, resilience, and toughness. The chapter describes the effects of stress concentrations on ductile metals under cyclic loads. Other topics covered include combined stresses, yield criteria, and residual stresses of metals.

Fracture is the separation of a solid body into two or more pieces under the action of stress. Fracture can be classified into two broad categories: ductile fracture and brittle fracture. Beginning with a comparison of these two categories, this chapter discusses the nature and causes of these failure modes. Some body-centered cubic and hexagonal close-packed metals, and steels in particular, exhibit a ductile-to-brittle transition when loaded under impact and the chapter describes the use of notched bar impact testing to determine the temperature at which a normally ductile failure transitions to a brittle failure. The discussion then covers the Griffith theory of brittle fracture and the formulation of fracture mechanics. Procedures for determination of the plane-strain fracture toughness are subsequently covered. Finally, the chapter describes the effects of microstructural variables on fracture toughness of steels, aluminum alloys, and titanium alloys.

The existence of austenite and ferrite, along with carbon alloying, is fundamental in the heat treatment of steel. In view of the importance of structure and its formation to heat treatment, this chapter describes the various microstructures that form in steels, the various factors that determine the formation of microstructures during heat treatment processing of steel, and some of the characteristic properties of each of the microstructures. The discussion also covers the constitution of iron during heat treatment and the phases of heat-treated steel with elaborated information on iron phase transformation, hysteresis in heating and cooling, ferrite and austenite as two crystal structures of solid iron, and the diffusion coefficient of carbon.